still have the stock air box?
make the opening bigger. Doing this on mine lowered the IAT and much better throttle response and I'm getting slightly more MPG.
I have a picture of the opening in my thread, link in my Sig- towards the ends of the pages.
My XJ has a 3 inch lift, 31X10.50 and basically stock everything else and I'm getting a min of 24MPG on the hwy. I'm doing the maintenance a little sooner then scheduled so all of the stuff is in prime shape.
And airing up the tires for HWY runs makes a huge difference, I put mine at 33 PSI- but I do see the middle wearing slightly more then the edges...

 

Cold air intake without the factory restrictions and less restrictive exhaust will help a bit.
Stock size street tires, no lift, drive like there's an egg between your foot and the accelerator....

 

Id run 4.10s with you running I-95 allot of the guys I have talked to say 4.10s give you stock feel with better mpg. Seems like they do good off road to I see them all the time on the beach with them.

 

haha thats awesome. (or be like this guy )